Behind the cut there are spoilers for both this week's episode (Stakeout) and the end of the season.
I no longer think it is Jenny who is leaving :-(
I think that with her being ill it's too obvious it's her. That we are being lulled us into false sense of security.
I now think it will be Tony, who was my second choice last time, but all I could come up with was he left to marry Jeanne, and that didn't seem to be twisty, etc. Now I think the whole twist, surprise and repercussions will revolve around Jeanne, La Grenouille and Jenny's obsession with him having killed her father, etc.
I think that Jeanne will blame Jenny for her father's murder - I'm not sure Jenny did commit it (in fact she probably didn't, maybe it was the CIA). However, Jeanne will believe she did and she'll try to kill Jenny (as I suggested in one my previous theories) but Tony will save Jenny's life and in doing so be killed himself. Jenny will get better and of course feel very guilty about Tony giving his life for her, and this can easily flow over into Season 6.
I hope I'm wrong, I really do. But, even if it's not Tony, I just have this strong feeling it won't be Jenny, as it's far too obvious now that it's her *sigh*
Of course it could be the classic double-bluff, make it so obvious it's her we think it's not, but it will be. But . . . (Wonders if TPTB are that smart/devious).
And of course it could all still be a rumour. However, I have heard elsewhere that it's true, not from Harriet admittedly, but . . . I do think it's true that someone is going.